Engines may be configured with various fuel systems for delivering a desired amount of fuel to a combustion chamber. Example fuel systems may include port fuel injectors for delivering fuel into an intake port upstream of a combustion chamber, and direct fuel injectors for delivering fuel directly into the combustion chamber. Still other engines may be configured with a multi-fuel injection system that includes, for example, each of a port fuel injector and a direct fuel injector for each engine cylinder.
One example approach for utilizing both port and direct injection during engine starting includes utilizing a port injection and split direct injection, such as described by Surnilla et al. in 20140297159, for example. Therein, split fuel injection is applied during start and cranking so that fuel of lower alcohol content is port injected and fuel of higher alcohol content is direct injected as one or multiple injections.
However, the inventors herein have recognized potential issues with such an approach. For example, as operating conditions change, the desired relative amounts of the port to direct injection ratio change as well as the ratio of the multiple direct injections. Such variations can be difficult to predict under all operating conditions, particularly when an operator may or may not intervene during the start with pedal adjustments. As a result, one or more of the injections may reach a minimum pulse-width limit of the injector, unexpectedly causing an undesired enrichment. And even when such situations can be detected, it can be difficult to properly schedule adjustments to compensate with the least amount of disturbance to vehicle operation and emissions.
In one example, the issues described above may be addressed by a method, comprising: during a cold engine start, injecting, during a single cylinder cycle, a port fuel injection, an intake stroke direct fuel injection, and a compression stroke direct fuel injection; and responsive to one of the direct injections reaching a minimum direct injection pulsewidth, reducing a ratio of port to direct fuel injection.
In this way, it is possible to appropriately control not only the ratio of port to direct fuel injection, but also the ratio of the split direct injections. For example, if multiple of the direct injections reach the minimum direct injection pulsewidth, the method can reduce the ratio of port to direct fuel injection while adjusting a ratio of direct injections to bring an amount of each of the direct injections closer to each other and while maintaining an overall fuel injection amount for the cycle. This can maintain the effectiveness of the split direct injections on engine starting performance. In contrast, if only one of the direct injections reaches the minimum direct injection pulsewidth, the method may reduce the ratio of port to direct fuel injection while maintaining a ratio of direct injections relative to one another, and while maintaining an overall fuel injection amount for the cycle. In this way, the longer the ratio of direct injections can be maintained relative to one another, the better the engine emissions can be managed during the transition, given that the unadjusted ratios may have been determined to provide the optimum emissions and fuel economy balance. Such operation can be particularly relevant when the port fuel injector is coupled to a high pressure port fuel injection rail that is pressurized at least partially via the high pressure fuel pump used also for pressurizing the direct injection fuel rail, although it is still relevant to lower pressure port injection rails pressurized only via a low pressure electric-motor driven lift pump.
A technical effect of controlling the port to direct injection ratio and/or direct injection split ratio may be to enable control of engine emissions and stable engine operation even if varying conditions unexpectedly cause one of the fuel injections to reach a minimum allowable pulsewidth.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.